Superheater



Nov. 30, 1943.

c. MclNTosH Re. 22,396

SUPERHEATER Original Filed Feb. 15. 1941 2 Sheets-Sheet 2" ATTORNEYS Reissued Nov. 30, 1943 UNITED 'STATES PATENT OFFICE SUPERHEATER Charles McIntosh, Detroit, Mich.

Original No.

Serial No. 379,029,

Claims.

This invention relates to superheaters and particularly to superheaters of the type intended to be located in the combustion chamber of a vapor generator, such as a steam generator, and directly exposed to the radiant heat and to the hot products of the combustion taking place therein.

In all types of superheaters heretofore employed, whether directly exposed to both the radiant heat and the convection heat of the combustion chamber or arranged interdeck so as to be shielded from the radiant heat and to rely almost entirely upon convection for superheating, difficulty has been experienced in maintaining a substantially constant outlet temperature of the superheated steam or other vapor at varying boiler loads, especially when the, range of variations is wide or the changes in demand sudden. In the prior art radiant type superheaters, which receive the greater part of their heat in the form of radiant energy from the re, a sudden increase in steam demand causes a falling oil. of the outlet temperature and, vice versa, a lighter than average demand results in an increase in the outlet temperature. On the other hand the outlet temperature in the convection type superheater, located nterdeck in the boiler, rises when the steam demand is heavy and falls of! when the steam demand is light.

Attempts so to control the gas ilow over the tubes of this last mentioned type of superheater, by manually controlled dampers and the like, as to adjust the heat input to the varying steam demands have not proved satisfactory because of the human element involved. Desuperheaters are also unsatisfactory, iirst, because they do not protect the structure from excessive heat and,

secondly, because many of them give, as an end product, a non-homogeneous mixture of saturated and superheated steam.

In modern steam power plants in which high total temperatures of the steam and high pressures are employed, such, for example, as a steam temperature of 900 F. and a steam pressure of 2000 lbs. per square inch, it is important that marked variations in the steam temperature be not permitted, since the temperature is already above the red heat of the metal of the tubes and marked variations in the temperature might cause serious damage to the steam generating plant as well as damage to the prime movers, such as steam turbines.

A general object of the present invention, therefore, is to provide a superheater, and particularly a superheater of the type which re- 2,309,706, dated February 2, 1943,

February 15, tion for reissue September 30, 1943,

1941. Applica- Serial No.

ceives its main heat in the form of radiant energy from the fire, in which not only can there be obtained a substantially constant outlet temperature of the superheated vapor, but in which the metal conduit through which the vapor travels and in which it receives its additional heat will be maintained at a temperature approximating that of the desired superheat temperature of the vapor, allowing, of course, for the heat drop through the metal to the vapor.

A particular object of the invention is to so control the temperature of the conduit or conduits through which the saturated vapor to be superheated passes, and in which it receives the additional heat, as to compensate for marked variations in the heat, both radiant and convection, to which the conduit is exposed. More particularly, the invention aims to effect such a controlled absorption of the heat, either radiant or convection, to which the superheating conduit is exposed, by means of a constantly owing Alicluid as essentially to shield the vapor to be superheated from excessive heating or, in other Words, to maintain, by absorption of excessive heat before it reaches the vapor to be superheated, a predetermined temperature relation -between the superheating conduit and the vapor passing therethrough,

Having regard to the foregoing objects, the invention contemplates so constructing and arranging a central liquid conduit, which is surrounded by a plurality of parallel vapor conduits each having a wall thereof in continuous metallic heat-exchanging relation to the liquid in the central liquid conduit, that the walls of the liquid conduit, which will be wetted to the required extent by a positive but controllable flow of liquid therethrough, extend between the vapor conduits, in integral heat-conducting relation thereto, to points where they provide highly conductive, short-circuiting by-passes to the liquid for heat received by the structure in excess of that required to maintain the vapor conduit walls at the proper temperature for the desired outlet vapor temperature.

The invention further contemplates so adjusting the flow of the liquid in respect to the temperature of the vapor as it is discharged from the superheating conduits as When the boiler with which the superheater is associated is in continuous operation, such control of the liquid in the central liquid conduit by the temperature of the superheated vapor will comprise, for the most part, varying the liquid to maintain substantially constant superheat temperature..

flow for 'the purpose of maintaining the desired constant outlet temperature with varying rates of steam demand or boiler load andwith the usual incidental varying heat releases in the combustion chamber. However, when starting up a boiler having a superheater embodying the present invention associated therewith, there will be no vapor owmg through the vapor conduits im;

made for control other than by the outlet'temperature of the vapor, both the vapor and liquid conduit-s would soon be dry. The invention, therefore, contemplates such auxiliary control of the liquid flow as to insure protective flow of liquid through the liquid conduit when there is no vapor now to protect the vapor conduits.

In particular, the invention contemplates the provision of three separate, but at times cooperative, means for controlling the ow of the temperature governing liquid through the liquid conduit, one of these means being governed in its operation by the outlet temperature of the supe-rheated vapor, another of these means being governed in its operation by the outlet temperature of the liquid or mixture of liquid and Vapor issuing from the liquid conduit and the third means being manually operated and used for the most part only when starting up a boiler with which the superheater is associated.

An important feature of the invention is the construction and arrangement of a central liquid conduit of such outside dimensions as to provide for the desired number and spacing of vapor conduits about it while at the same time providing a cross-sectional area of the liquid now passage therein such as to insure the desired rate of flow and wetting effect without too much pump ca pacity. Other important features are the novel manifold construction, the novel arrangement of the control of the liquid flow between the circulatin-g pump and the liquid conduit and the simple and convenient means for connecting the superheater to the various parts of the boiler as sociated therewith whereby it may readily be removed for cleaning, repair or replacement.

with the accompanying drawings in which Figure 1 is a view showing a superheater embodying the present invention installed in a boiler of the low head type;

Figure 2 is a longitudinal section through one of the two manifolds connected to the ends of a superheater unit;

Figure 3 is a section on ure 2;

Figure 4 is a longitudinal ing a modied construction and Figure 5 is a section ure 4.

In the illustrative embodiment of the invention, designed Y particularly for superheating steam, the water and steam conduits of the superheater, which are shown in section in Figure 3J comprise a tube 2 having therein the water passage 4, this tube 2 being of a diameter and of a wall thickness the line 3 3 of Figsectional detail showof the liquid conduit,

substantial number of steam tubes 6 having therein the steam passages 8. Illustrative dii-nen- On the line 5 5 of Figvided at each end with sions for the tube 2 are an internal diameter of 21/8 inches with an original wall thickness 4of about 1/2 inch. As shown, this tube 2 has milled in its outer surface seven recesses In conformed to and arranged to receive the steam tubes 6 which may be, for illustration, of an outside diameter of 11A; inches and an inside diameter of 1% inch. With the dimensions given, recesses I0 for seven steam tubes 6 can conveniently be provided in the outer surface of the tube 2 without 'reducing the wall thickness at the point I2 too much. With the dimensions given and the recesses formed as shown in Figure 3, the thickness of the wall at the point I2 will be in the neighborhood of 1/8 inch, which is suiiicient to sustain ordinary boiler pressures. For higher pressures greater wall thicknesses may be provided.

'I'he recesseslIU having been milled in the periphery of the tube 2 to fit, as closely as possible, the outer surfaces of the tubes 6, the tubes 6 are then welded in their positions on the tube 2 by welds I 4 'which form integral connections between each of the tubes 6 and the portions of the tube 2 lying between the recesses I El.

It will be seen that the welds I4, forming integral connections between the tubes 6 and the tube 2, provide highly conductive short-circuiting paths directly tothe water in the conduit 4 for either radiant yor convection heat impinging upon the'tubes 6 and the welds I4. The eifect of the provision of these by-passes for the heat will bev more fully set forth hereinafter.

The assemblage of tubes just described is proa manifold such as is illustrated in section in Figure 2 of the drawings. The illustrative manifold comprises a casting I6 having therein a steam chamber I8 which communicates with each of the passages 8 in the tubes 6. The casting I6 is provided with openings 20, 22 and 24, the opening 2D being adapted to receive the end of the assemblage of superheater and liquid tubes, the opening 22 being adapted to receive a nipple 26 provided with a connecting ange 28 in the form of a collar weldreceive a short tube section or nipple 3U extending through the steam chamber I8 into the passage 4 of the tube 2 into a collar welded thereto. Welds 3d secure the nipples 2S and 30 in their respective openings 22 and 24 and also secure the collars or ilanges 2S and 32 respectively to the nipples 26 and 3U. Welds 34 also secure the nipple 30 in its position in the tube 2. It will be understood that the collars 28 and 32 might be mounted on the nipples 26 and 30 and confined thereon by expanded nipple ends in a Well-known manner.

In order to t the tube assembly to the opening 2U in the casting I6, the Welds III at the end of the assembly are increased in thickness until they completely ll the spaces between the tubes and until the end has an approximately circular outline which is then machined or ground to fit the circular opening 2B. After this tube assembly is inserted in the opening 20, the header casting I6 is secured to the assembly by welds 36. Y

The superheater unit, constructed inthe manner just described, may be inserted in the com-4 bustion chamber 38 ofv a boiler, for example one the passages 8 in the superheating tubes 6. It

of the low head type, such as shown in Figure 1, in any suitable position to expose it to the heat released in said chamber, particularly the radiant heat, it being understood, of course, that a number of these units sufficient to effect the superheating of the maximum boiler output may be arranged side by side in the combustion chamber.

As shown in Figure l, the superheater unit is inclined to the horizontal and the flow of both the steam and the water is preferably upward through the unit although it will be understood that, if desired to meet certain conditions, the steam and water might pass through the unit in counterflow relation to each other. As further shown in Figure l, the superheater unit extends through both furnace walls 40 and 42 and the headers are located outside the combustion chamber. At its lower end the header of each superheater unit has its flange 32 connected to a corresponding flange on a nipple 44 branching off from a water manifold 45 connected to the `pump 46 while the flange 28 is connected to a corresponding ange on a nipple 48 branching off from a steam manifold 49 connected by pipe 50 to the steam space in the drum 5|. The header at the other end of each superheater unit has the flange 32 connected to a corresponding flange on a nipple 52 branching from a water manifold 53 connected by pipe 54 to the steam and water separating space in a drum 55 and has the flange 28 connected to a corresponding flange on a nipple 56 branching from a steam manifold 58. The steam manifold 58 is connected to the pipe '60 for delivering the superheated steam to the point of use.

If the flanges 28 and 32 are welded to their nipples 26 and 3D as shown in Figure 2, then, preferably, the cooperating flanges on the nipples 44, 48, 52 and 56 will be loosely mounted on said nipples to facilitate making the connections. f The intake 62 for the pump 46 is connected to the water drum 64 of the boiler and the discharge 6B of the pump 46 is connected through three branches 68, 1D and 12 with a common junction pipe 14 which, in turn, is connected to the water header 45.

In the branch pipe E8, between the discharge E and the junction pipe 14, is a valve 18 adapted to be controlled thermostatically through connections to a thermostatic element 18 in the thermometer well at one end of the manifold 58. These operating connections may be of any suitable or well known type, such as a connection 88 to a pneumatic relay 82 connected by an air tube 84 to the diaphragm valve operating mechanism 8B.

In the branch 12, between the outlet B6 and the junction pipe 14, is another thermostatically controlled valve 88 arranged to be controlled by suitable connections to a thermostatic element 9D in the water outlet manifold 53, said connections comprising a lead 92 to a pneumatic relay 94 and an air tube connection 9'6 to a diaphragm valve operating mechanism 88. i

In the branch 10, between the discharge ES and the junction pipe 14, is a hand operated valve |00 designed principally for use when the boiler, with which the superheater is associated, is being started up.

From the foregoing description it will be seen that when a boiler is operating under load conditions, that is, when steam is being constantly delivered for use through the steam line En, there will be a constant flow of steam through will further be seen that the amount of the superheat imparted to this steam will be controlled by the water flowing through the pas- 'sage 4 in the central tube G and that the rate of flow of the water will be governed by the amount of cooling action required to maintain the tubes E at the proper superheating temperature, this flow necessarily varying somewhat with the variations in the boiler load or, in other Words, with variations in the demand made upon the boiler.

i If, for example, there be a sudden increase in steam demand, so that the rate of flow of the steam through the tubes 6 is so fast that, even with the increase in heat release in the combustion chamber usually accompanying such increased demand, there is not sufficient time for the saturated steam to receive the required superheat at the heat exchange rate provided by the then cooling action of the water flowing through the tube 2, any drop in steam temperature thus caused will act upon the thermostatic element 'I8 in the thermometer well in manifold 58 and cause the valve 1S to move toward its closed position, thus cutting down the rate of flow of the Water through the central tube 2 and thereby reducing the amount of short-circuiting or `:ry-passing of the heat impinging upon the tubes 6 and upon the welds I4 connecting these tubes integrally with the central tube 2. Vice versa, with the falling off of the demand for steam and the thus retarded movement of the steam through the tubes 6, with a corresponding greater opportunity to receive superheat, the tendency of the steam to emerge from the tubes G at a higher temperature will serve, through the thermostatic element 18 and its connection to the valve 1E, to open the valve 16 and permit a greater flow of water through the central tube 2 and thus a greater cooling action upon the tubes 6 or, more technically speaking, a greater by-passing to the central tube 2 of the heat impinging upon the tubes 6 and upon the welds I4 which connect the tubes 6 with the tube 2.

f Ordinarily during the operation of the boiler the control of the flow of the water through the central tube 2 by variations in the temperature of the superheated steam, as it is recorded by the thermostatic element 18, is sufficient both to secure the desired constant superheat and to insure protection of the structure from overheating. When starting up the boiler, however, and under exceptional condit1ons, further control of the flow of water through the central tube 2 by means of the outlet the water, or of the mixture of steam and water, as it is received in the manifold 53 is desirable to 'prevent injury to the metallic structure and for this reason the thermostatic element 80, with its connections to the valve 88, is provided.

It will be apparent that when starting to heat up a cold boiler there will be no steam pressure, no steam flow through the steam line '68 and therefore no flow through the superheater tubes E. Moreover, it will be evident that any condensed steam that may still be in the superheater tubes 6 will quickly be vaporized and thus soon leave these tubes substantially dry. In the central tube 2 there will ordinarily be some water left from the previous operation of the boiler but, in the absence of water supplied from the manifold 45 under the action of the pump 45, this water in the central tube 2 will quickly be vaporized and pass over as steam through the pipe 54 into the drum 55. Also, because of the cold condition of the structure at starting, the thermostatic elements 78 and 9i) will operate to maintain the valves i and 88 in their closed water through the central tube 2 at the time-of starting unless the hand valve IUD be opened.

Having regard to the foregoing conditions surrounding the structure at the time of .starting valve 88 and increase the flow of water through the central tube 2. The temperature above which the thermostatic element SD will operate to open the Valve 88 will ordinarily be so selected that, in the normal operation of the superheater, the thermostatic element 9B will not tend to increase the flow of water through the central tube 2 by opening the valve 88 unless there is a tendency to generation of steam in wetted surface in the conduit 4 at this end.

In order that the central tube 2 may accommodate on its periphery a substantial number of superheater tubes E, it is essential that it be of substantial diameter. Even with a wall of substantial thickness this forced through the passage 4 by a pump 46 of a given capacity. v

In order to secure the desired velocity ofilow in the tube 2 without requiring a pump 46 of too great capacity, the modified form of water con- The dimensions of the spacers 04 are such that the tube |32 may readily be inserted in or removed from the tube 2.

To prevent substantial ow of the water through the tube |62 1t 1s provided at one end,

permitted to ow through the passage 4 in the tubev2 when the tube |02 is in position therein will have a cross sectional area equivalent to the difference between the cross sectional area of the e 4 and the area of a circle having the outer diameter ofthe tube [62.

however, when the passages 4 in the tubes 2.

As hereinabove suggested, when boiler from its cold condition, the

starting up the hand-operated is being made, steam will iiow through the superheater tubes 6. E'ven before this takes place, the hand-operated valve le@ may usually be closed, since the thermostat 953 in the manifold 53 will ordinarily have operated to insure circulation of water through the tubes 2 suflicent to protect the structure.

As soon las steam is flowing through the super- 2 to the thermostat T8 in the manifold 53.

When operating under varying demand, if the amount of steam owing through the tubes 5 increases, tnus tending to cool down the walls of slightly lower temperature of the superheated steam will cause the thermostatically operated valve 'It to close slightly, thereby reducing the flow of the water through the tubes 2. The resulting raised temperature of the tubes B will quickly bring the temperature of the super- Although, in the illustrative embodiment of the invention the water for controlling the superheat temperature by Iiow through the tubes 2, 1939, for Letters Patent for Superheaters.

What is claimed as new is:

1. Apparatus for raising s turated vapor owing therethrough to a subsbtantially constant superheat temperature comprising, in combination, a central conduit for liquid, a plurality of parallel vapor conduits arranged about said liquid conduit and each having the wall thereof integrally connected to a part of the wall of said central conduit in such manner as to provide a highly conductive by-pass to the liquid in said conduit for heat impinging upon the structure in excess of that required for superheating, and means, governed in its effective operation by the outlet temperature of the superheated vapor, for producing a positive and continuous flow through said liquid conduit of a wall-wetting stream of liquid of a volume and velocity adequate only to absorb said excess heat of the structure, said liquid and said vapor passing through said structure in parallel now and said structure providing no immediate integral heat-conducting path between the vapor in said conduits and the heat-absorbing liquid.

2. Apparatus according to claim 1 in which the main stream portion of said liquid conduit is of sufficient circumference to cooperate with at least flve surrounding vapor conduits and is of annular cross section in order to provide rapid flow of improvements in the heat-absorbing liquid in said liquid conduit.

3. Apparatus according to claim 1 in which a tube concentrically positioned in said liquid conduit and provided with means for resisting flow through its passage deflnes a conduit of annular cross section for the main liquid ow, said conduit being of suflcient circumference to cooperate with at least five surrounding vapor conduits and the reduction in the stream cross-section eifected by the concentric tube serving to accelerate the rate of flow of the heat-absorbing liquid while still maintaining it in immediate heat-exchanging relation to those parts of the structure which serve to divert excess heat from the vapor conduits.

4. Apparatus according to claim 1 in which additional thermostatic controlling means are provided whereby the effective operation of the liquid flow-producing means is governed also by the outlet temperature of the liquid.

5. Apparatus according to claim 1 in which intake and discharge manifolds supply a plurality of superheaters of the described construction and in which additional thermostatic controlling means are provided whereby the input into the liquid intake manifold is controlled also by the mean temperature of the liquid in the liquid discharge manifold.

CHARLES McINTOS-H. 

